Method for subsurface aerated treatment of wastewater

ABSTRACT

The performance of a leach field of a septic tank type wastewater treatment system and other analogous devices is enhanced, maintained or rejuvenated by flowing air or other active gas through conduits of the system. Air is flowed serially through cesspools, leaching chambers, perforated pipes in stone filled trenches, leach pits and the like, and the adjacent soil where wastewater treatment takes place. In alternate embodiments, conduits are pressurized or evacuated; and, auxiliary pipes are buried in vicinity of the conduits. An air mover creates a differential pressure sufficient to effect a significant pressure differential with atmosphere and to effect a desired physical or biochemical change in the soil adjacent the conduits. A typical pressure will be around 7-8 cm (about 3 inch) water column. If the soil is saturated, the air pressure will push water from the soil, as well as change the gas composition in the soil. The flow of wastewater may be alternated with the flow of air. Different valve devices and piping configurations are used to manage the desired flow of air and wastewater.

[0001] This application is a continuation of patent application Ser. No.10/292,185, filed Nov. 12, 2002, which was a continuation in part ofpatent application Ser. No. 09/526,381, filed Mar. 16, 2001, now U.S.Pat. No. 6,485,647; and claims benefit of Provisional Application SerialNo. 60/125,070, filed Mar. 17, 1999.

TECHNICAL FIELD

[0002] The present invention relates to the subsurface disposal ofwastewater (sewage); in particular, to disposal of wastewater by meansof cesspools, septic tank type systems and associated leach fields.

BACKGROUND ART

[0003] Subsurface wastewater disposal systems, commonly called septictank systems or septic systems, are widely used for on-site processingof wastewater from dwellings and other smaller volume wastewatersources. Typically, wastewater is delivered via a wastewater line to aseptic tank for primary processing. The septic tank effluent, orwastewater, is flowed to a leaching system for secondary processing bymeans of distribution pipes. The leaching system, also commonly called adisposal field, leach field, or infiltration field, typically comprisespermeable soil of the earth and some sort of excavation in the soilwhich is filled with stone particulate such as crushed stone or coarsegravel (typically 2.5 cm in dimension) and or a mechanical component,the function of which is to convey wastewater through a conduit, toinfiltrate it into the soil.

[0004] The principal function of the septic tank is to effect primarywastewater processing by engendering physical separation and retentionof solids which are lighter and heavier than water, typically bysettling and baffling. Solids, which settle out as sludge, are mostlydecomposed by action of bacteria in a typically anaerobic environment.Gases, which are generated in the process, are vented to atmosphere. Thewastewater from the septic tank is typically conveyed to the leach fieldby passing it through a distribution box and piping which channelswastewater to the leach field trenches, in a predetermined fashion. Thewastewater is supposed to be free of solids of significant size. It willcontain suspended solids of fine size, microorganisms such as bacteriumand viruses, and various chemical constituents.

[0005] The purpose of the leach field is generally to cause thewastewater to be treated or renovated, so it can be benignly returned tothe hydrologic cycle that characterizes the movement of water into,through, and from soil beneath the surface of the earth. What follows isa simplified version of certain conventional ways of looking at leachfield operation phenomena, to provide a conceptual framework forappreciating the invention. It is not intended to be comprehensive norlimiting.

[0006] As the wastewater travels from within a leach trench and throughthe soil in a properly functioning system, it is subjected to naturalchemical and biological processes within a “zone of influence”, whichmay extend 30-120 cm from the trench interface with the soil. Atraditional leach field is comprised of a trench filled with small (2-3cm) stone pieces. A perforated pipe runs through the stone, deliveringthe wastewater along the trench. A popular modern type of leach fieldcomprises a series of interconnected arch shaped molded plastic chambershaving perforated walls, such as leaching chambers sold under theInfiltrator brand name. See U.S. Pat. No. 5,401,116 of J. Nichols, andU.S. Pat. No. 5,511,903 of J. Nichols et al. Typically, Infiltrator®chambers are directly buried in a trench in substitution of thestone-and-pipe leaching device.

[0007] The leach field must have sufficient capacity to receive andproperly process the anticipated flow of wastewater. The steady statecapacity, or the infiltration rate, of a leach field is a function ofthe resistance to wastewater flow of the surfaces of the trench and thesurrounding soil, as such may be influenced by hydraulic phenomena otherthan permeability, such as capillary action. For illustration here, onlythe sidewall of the trench will be now discussed. If distilled water isprocessed in sterile soil of a leach field, the infiltration rate ispurely a function of the mechanics and hydraulics of the soil. However,in that wastewater contains organic substances, over time, an active,stable, moist biological crust layer frequently grows on surfaces. Ofparticular interest is the crust layer which occurs on a trench sidewalland within the nearby soil, especially when the layer tends to blockopenings in leaching system conduits.

[0008] The crust, also commonly called a biomat or biocrust, is anorganic layer, typically 0.5-3 cm thick. It is normally less permeablethan the surrounding soil. Thus, the biomat often significantlydetermines the long-term steady state infiltration capacity of a leachfield. The biomat also serves as a filter for bacteria and somesuspended solids. In a properly functioning system, the surrounding soilto remain desirably unsaturated and aerobic, thus enabling antibioticattack of any pathogenic bacteria, and more importantly, chemicalreactions involving free oxygen. Biomat is thought to aid in filteringthings which enter the influence zone. Nitrogen, discharged in humanwaste, is characteristically passed through any biomat, predominantly asammonium (NH₄ ⁺), to be nitrified, or converted to nitrate (N0 ₃) form,in the aerobic environment of the influence zone and adjacent soil.Foreign constituents in the wastewater may also sorb and or react withsoil constituents; or they may ultimately be only diluted upon return tothe ground water. As the wastewater is renovated in the influence zone,it moves mostly outwardly and downwardly toward the ambient water tablein the earth. Some water may move upwardly into the vadose above thetrench, by capillarity, evaporative-uptake and plant-uptake. It isusually required that the bottom of the leach field trench be aparticular distance above the ambient water table, because sub-optimalwastewater treatment conditions exist in the extremely moist soil, thecapillary fringe, just above the water table.

[0009] In a properly designed, used and maintained septic tank disposalsystem, once biochemical equilibrium is reached, the capacity of theleach field remains stable insofar as infiltration or leaching capacity.A long term infiltration rate, or liquid acceptance rate, characteristicsoils of southern New England, USA is about 8-32 liters/m²/day. However,too frequently, a septic tank system will demonstrate insufficientinfiltration capacity. Typically, a failure is manifested by escape ofwastewater to the surface of the soil, or by a substantial backing up ofwastewater in the wastewater line. One cause of failure can be grossflow of solids from the septic tank into the leach field piping orchamber system, and blockage of the perforations in such components. Thetypical best remedy for such is to replace or extend the leach field.Failure can also be manifested by an inability of a given system tohandle normal peak loads of wastewater which were handled in the past,and by inadequate purification of the wastewater in the influence zone,resulting in pollution of the groundwater. And, even if a system has notfailed, it is desirable to guard against failure by having the greatesteconomically feasible margin of safety against failure.

[0010] Among the known causes of some failures are the following. Thedesign of the system has become inadequate for the current conditions,either due to growth of a very heavy biomat, a changed character ofwastewater, or changed conditions within the soil in the influence zone.For instance, the biological oxygen demand (BOD) of the wastewater mayhave been increased, or the ambient soil conditions changed, so that thedesired biochemical conditions for stable aerobic function in theinfluence zone are no longer obtained. An accumulation of unreactedwastewater within the influence zone limits oxygen transport. Thus, acascading type of failure mode may ensue, wherein the influence zonegets bigger and bigger as it gets less and less effective.

[0011] Cesspools, favored in some regions, avoid the use of septictanks. Untreated wastewater from a source is dumped into and partiallytreated by natural processes in the pool of an underground pit; and, thethe wastewater infiltrates into the influence zone of soil surroundingthe pit for further treatment. Phenomena and problems similar to thosedescribed for leach fields will exist in cesspool influence zones.

[0012] Thus, there is a need for alternatives to the costly or sometimesphysically impossible remedy of adding to or replacing the leachingsystem. And, if good technology is at hand, the possibility arises forputting in a smaller system initially and reducing cost, for providinggreater margin of safety in any given system, or for allowing growth inuse of an existing system.

[0013] Various approaches to enhance the capacity of leaching systemshave been tried, reflecting different concepts of both failure andremedy. Chemical remedies in the forms of solvents, enzymes, and otherproprietary formulations, for deposit into the wastewater line withwastewater, are commercially sold, but most are disdained or ignored byprofessionals. U.S. Pat. No. 5,588,777 of Laak discloses the injectionof soap into the leach field. U.S. Pat. No. 5,597,264 of Laak disclosesa method of periodically back flushing the leach field with water. U.S.Pat. No. 4,333,831 of Petzinger describes the type of problem mentionedabove, solving it by using evaporation chambers in substitution of anyleach field. U.S. Pat. No. 3,907,679 of Yost describes a system in whichlow pressure air is forced through a septic tank and then into a longcoil of wastewater piping, so wastewater evaporates into the air and isdischarged to atmosphere. U.S. Pat. No. 3,698,194 of Flynn describes howair is blown into a conduit of a leach field and vented from risers atthe remote end of conduit, to cause evaporation of liquid in, and to dryout grease in, the conduit, during periods when the conduit is not beingused for wastewater treatment. U.S. Pat. No. 4,013,559 of Johnsondescribes how air is introduced into the septic tank, flowed throughunique vertical concrete panel leaching system units, and thendischarged to atmosphere, to encourage aerobic conditions in wastewaterwithin the panels. However, none of these prior art technologies seem tohave found wide spread use. Thus, there is a continuing need for newways to enhance the design and performance of leaching fields, both asthey are originally installed and for when there are in need ofrejuvenating.

SUMMARY

[0014] An object of the invention is to provide means for improving thefunction of septic tank type disposal systems and leach fields, toremedy failures, or forestall failure, or improve performance, in waysthat are economical and practical. A further object of the invention isto effect desirable biochemical and physical conditions within theinfluence zone of a leach field. A still further object is to provide away of sustaining or rejuvenating leach field performance while at thesame time enabling continuous use of a septic tank type wastewatersystem.

[0015] In accord with the invention, when wastewater is flowed from aprimary wastewater processing unit, such as a septic tank, through aconduit, and into an influence zone in the soil, a significant pressuredifferential with atmospheric pressure is created, as gas, comprised ofair or other biochemically active gas, flows between the conduit and theinfluence zone, in an amount effective for physical and or chemicalchange within the zone. In further accord, the flow of active gas issufficient in amount to make the composition of gas within the influencezone effectively different from the composition which existstherewithin, in the absence of such flowing. Thus, if the leach field isfunctioning properly, the invention maintains or improves such; and, ifthe field is failing, the invention will restore part or all of thefunction. In one embodiment, air flows from a conduit, into and throughthe influence zone, in the same direction as the wastewater flows. Inanother embodiment, air flows from the influence zone and into theconduit. In both embodiments, an air mover such as a blower or vacuumpump establishes a significant pressure differential in the influencezone.

[0016] In a preferred embodiment, a blower pressurizes the systemconduits relative to atmosphere, and air flows through the influencezone, the adjacent soil, and ultimately back to atmosphere. If theinfluence zone is saturated, the pressure of air causes the water in theinfluence zone to physically move away from the conduit and the zone isde-saturated. When not fully saturated, the pressure of air flow causesphysical gas exchange, to make the composition of gas in the influencezone more near that of atmosphere. In another embodiment, air flowssimilarly, but from an unpressurized conduit to an auxiliary pipe whichis buried in the soil and maintained at below atmospheric pressure. Inanother embodiment, and air mover lowers the pressure of gas in theconduit and air flows from atmosphere, through the soil and influencezone and into the conduit. In another embodiment of the invention, airflows from a pressurized auxiliary pipe buried in the soil adjacent thetrench, and into a conduit vented to atmosphere. In another embodiment,air is introduced into the bottom of the leaching trench by a pipediffuser or by pipes which run lengthwise within the trench. Inpreferred practice, for a wastewater system embodying typicalconventional soils, the differential air pressure between the conduitand atmosphere is at least 2.5 mm, preferably about 7.5 cm or more,water column, in order to produce a desired level of biochemicallysignificant flow through the influence zone. When, in preferredembodiments, air is flowed from a conduit into the influence zone, thepressure in the soil of the influence zone, about 15 cm from the innerboundary of the influence zone, will be at least about 0.03 mm watercolumn, more preferably at least 0.8 mm.

[0017] In further accord with the preferred process of the invention,the influence zone of a deteriorated system is substantially anaerobicin character, and flowing of air or active gas causes the change so thatit becomes predominantly aerobic. In still further accord with theinvention process, the quantity of air or other gas which is flowed intothe influence zone provides oxygen substantially in excess of thestoichiometric quantity which is required for oxidation of theoxidizable constituents in the wastewater, as such constituents aretypically determined by measurement of Oxygen Demand, in particularBiological Oxygen Demand (BOD). Optionally, a gas or liquid substance isadded to the air to enhance biochemical activity.

[0018] In still another embodiment, the auxiliary pipe is buried underthe trench or is within the trench. A membrane is optionally placedwithin or on the soil, to control the direction in which air travelsfrom or to the soil surface. The air flow of the invention may bemaintained continuously or intermittently, with and without simultaneousflow of wastewater in a preferred, practice of the invention, by meansof a control system. To ensure good functioning of a system, a lowvolume of air is continuously flowed into the wastewater system and theair moves through the influence zone contemporaneously with wastewater.

[0019] In further accord with the invention, apparatus for treatingwastewater is comprised of a primary unit, such as a septic tank orother kind of reactor for primary processing of the wastewater, a leachfield, for receiving wastewater effluent of the primary unit, where theleach field is comprised of a trench in the soil, a conduit within thetrench, and soil adjacent the trench comprising an influence zone; and ameans, such as a blower or vacuum pump, for producing a pressuredifferential between the conduit and the adjacent soil, where thepressure differential is significant enough to effect a physical change,such as forcing water from the influence zone soil, or to effectbiochemically significant change in the biochemistry of the influencezone.

[0020] In preferred apparatus embodiments, there is a means, such as amechanical check valve or a water trap, in the pipeline of thewastewater system, so the effect of applied pressure or vacuum islimited to localized parts of the wastewater system. In one instance,there is a check valve in the distribution pipe, which runs from aseptic tank or the like to a distribution box, or other distributionpiping, and air pressure is injected at one or more selected points inthe distribution piping or conduits. In another instance, there is acheck valve in the wastewater line downstream of the stack vent andupstream of the point at which pressurized air is injected. In stillother embodiments, pressure or vacuum is applied to the wastewater linerunning into the septic tank and a check or other valve is presentupstream of the point of connection to the wastewater line of the bloweror vacuum pump source of differential pressure. In another embodiment, ablower is in the stack vent of the system. Use of the valve meansenables use of the system for processing wastewater simultaneously withuse of air flow. A check valve bypass line, temporary storage reservoirand pump are optionally in the wastewater line to further aid in theobjective of continuous use. The duration or periods during which air isflowed is optionally controlled by a control system which senses thecomposition or pressure of gas or liquid in vicinity of the influencezone or elsewhere in the wastewater system.

[0021] In a further embodiment of the method of the invention, theapparatus is configured so that there is a void space above the soilsurface of the influence zone, through which wastewater flowsdownwardly. For instance, the void might be the space within an archshape chamber or the spaces amongst stones within a trench. The water isfirst flowed in sufficient quantity and rate until it accumulates as apond above the soil surface. The air pressure is applied to the void, togive impetus to the natural flow of water. Then, the application of airpressure is ceased, and either the water flow is resumed right away, orthere is a period of quite time which is substantially longer than thetime of applying air pressure. The cycle may be repeated continuously.The process saves energy by decreasing the duration of air moveroperation.

[0022] Preferably, the amount of air or other gas provides a quantity ofair per unit time of system operation which quanity is many timesgreater, e.g., 10 to 25 times or more, than the quantity whichtheoretically would satisfy the biological oxygen demand of thewastewater.

[0023] The invention is effective in improving the operation of leachfields in a cost-effective way. Leach field performance and biochemistryare improved and maintained through use of the system. The invention canbe applied to existing installations and new installations. It is quiteuseful for rejuvenating the function of a system which has been eitherunder-designed or over-used.

[0024] The foregoing and other objects, features and advantages of thepresent invention will become more apparent from the followingdescription of best mode embodiments and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025]FIG. 1 is a perspective view of the basic elements of a prior artseptic tank wastewater system, having a composite of leaching fieldtrench types.

[0026]FIG. 2 is a elevation cross section through the pipe and stonefilled trench portion of the leach field of the system shown in FIG. 1.

[0027]FIG. 3 is a elevation cross section through the arch shapeleaching chamber-filled trench portion of the leach field of the systemshown in FIG. 1.

[0028]FIG. 4 is a semi-schematic, part-cross sectional, side elevationview of a septic tank type wastewater system having means for creatingpositive pressure gradient and outward air flow in the soil adjacent theleach field trench.

[0029]FIG. 5 is a semi-schematic cross sectional end view of a portionof a leach field, analogous to the views of FIGS. 2 and 3, showing howpressure-vacuum auxiliary pipes are buried in the soil laterallyadjacent the chamber-filled leach field trenches. It also schematicallyillustrates an associated control system.

[0030]FIG. 6 is a view analogous to FIG. 5, showing one of a pluralityof pipe and stone filled trenches having an underlying auxiliary vacuumpipe; together with a graph showing how negative pressure varies withdepth within the soil and apparatus shown in the left of the Figure.

[0031]FIG. 7 is a view analogous to FIG. 5, showing one of a pluralityof chamber filled trenches with one of a multiplicity of spaced apartpressure-vacuum auxiliary vertical pipes adjacent the trench.

[0032]FIG. 8 is a semi-schematic elevation view illustrating how apressurized air line and a check valve are positioned in the wastewaterline upstream of a septic tank through which air flows.

[0033]FIG. 9 is a view like FIG. 8 showing a J-trap check valve used insubstitution of the mechanical check valve shown in FIG. 8.

[0034]FIG. 10 is a view like FIG. 8, showing a check valve in a bypassline for a valved wastewater line.

[0035]FIG. 11 is a view like FIG. 10, showing a reservoir and pump forreceiving and forcing wastewater downstream into the septic system whileit is pressurized.

[0036]FIG. 12 is a view like FIG. 10, showing a variation on theapparatus illustrated in FIG. 11.

[0037]FIG. 13 is a fragmentary view like the view of FIG. 4, showing ablower positioned in the stack vent line.

[0038]FIG. 14 is a view like FIG. 3, showing an oblong air distributiondiffuser lightly buried in the soil beneath the bottom of a leachingchamber.

[0039]FIG. 15 is a view like FIG. 2, showing two air distributionperforated pipes within the stone of the trench.

DESCRIPTION

[0040] Reference should be made to the Background section hereof for adescription of various components, processes and environment whichrelate to both typical septic tank wastewater systems and the invention.FIG. 1 illustrates components of a typical septic tank wastewatersystem, familiar in the prior art. Wastewater flows through wastewaterline 18 from a dwelling or other source to a septic tank 20. Wastewaterflows from tank 20, through a distribution system. In particular, thewastewater flows through distribution pipeline 22, to distribution box30; and, then through further distribution pipes 56 to the leach field40. FIG. 1 shows a composite of two familiar types of leaching fieldconstruction. FIG. 2 and 3 respectively show elevation cross sectionviews through each of the two types. In two branches, or laterals, ofthe leach field 40 which is shown, a trench 35 is filled with crushed ornaturally small stones 36 typically about 2.5 cm in dimension,(hereafter referred to as “stone”); and, a perforated pipe 32distributes wastewater along the trench. The wastewater issuing from thepipe 32 may be temporarily stored in the voids within the stone; and, asindicated by the arrows 54, it then flows into the soil 38 (also calledsoil profile) beneath the surface 42 of the earth through the bottom andor side walls of the trench. A typical biomat 44 forms on and within thesurface of the trench. Additional biomat, not shown, will typically bepresent on the stones in the trench, and may be present to such anextent as to run like a membrane across stones which lie at theperforations or openings of the pipe. While typical, a biomat will notnecessarily be present in a wastewater system.

[0041] Referring to FIG. 3, in one branch, or lateral, of the leachfield 40, the trench is filled by a string of interconnected molded archshaped plastic leaching chambers 34, such as Infiltrator® chambers. Inmany respects the functioning of the chamber system is similar to thestone filled trench and thus will not be repeated. Wastewater flows intothe hollow interior of the chamber from pipe 56, where it may be storedtemporarily, and it then flows into the soil, out the open bottom wallof the trench and through perforations in the sidewall, as indicated byarrows 54. The chamber defines and maintains the trench, and providesthe conduit means for distributing wastewater along the trench.Sometimes, a pipe, which is a continuation of line 56, runs along thelength or a chamber interior peak to abet distribution of wastewaterwithin a string of interconnected chambers. The side walls of trench 35are defined by the chamber walls and the bottom is parallel to the baseof the chamber. Sometimes, the trench is made larger than the chamber,and crushed stone surrounds the chamber. From the foregoing it will beappreciated that both the chambers 34 and perforated pipes and conduitswhich both convey and disperse wastewater at different locations.

[0042] In both types of popular leach field constructions theinfiltration rate into soil is often limited at least in part by thepresence of one or more biomat layers. And, in both types there will bewithin the soil adjacent to the trench an influence zone 50, having anominal outer boundary 52, where the wastewater is (or should be, in aproperly functioning wastewater system) largely renovated, orbiochemically converted into a more environmentally benign form, priorto re-introduction into the ground water. The geometric definition ofthe influence zone is somewhat arbitrary and it can vary in dimensionwith time, as will be appreciated from the discussion in the Backgroundand herein. In the drawings here, the outer boundary 52 is imaginary andnot intended to represent any limiting dimension or proportion. Whilethe invention is described in terms of soil of the earth, it will beunderstood that such term comprehends installations comprised in wholeor part of artificial porous material such as sand and gravel and otherparticulate media.

[0043] The distribution portion of the FIG. 1 system includes a typicaldistribution box 30, which is intended to balance flow between thebranches of the system. In some septic systems there is only one branch,or several legs of the leach field are connected in series, in whichcase the distribution box is omitted, and the invention will beunderstood as being applicable in obvious ways to such systems. Thereare other commercial and non-commercial devices which are useful asconduits, in substitution of the stone filled trenches and chambers inleach fields; for instance, concrete galleries, leaching pits, alsocalled “dry wells”, and drip line, as used in irrigation systems. In thegenerality of the invention herein, chambers and stone-trench pipes, drywells, galleries, and all other substitutional devices—whethersurrounded with small stone or buried directly in soil, are allconsidered conduits of fluid, within a context that some serve otherfunctions as well. For example, cesspools and injection wells are alsoconsidered as comprising conduits and as functioning in part at least asleach fields. Cesspools are devices that function as both a primary unitand a leaching unit. Typically, raw sewage is introduced directly fromthe source, and as biochemical action takes place in the pool, thewastewater percolates into the surrounding soil. In injection wells,wastewater is pumped into the earth through a vertical pipe so itdisperses into material beneath or around the pipe. Most of the rest ofthe description here uses the example of leaching chambers.

[0044] A main part of the invention comprises pressurizing or evacuatingleach field conduits, relative to atmosphere. Pressurizing is describedfirst. FIG. 4 shows a semi-schematic side elevation view of a gravityflow septic tank system, which is an improvement on the essential systemshown in FIG. 1. A wastewater line 18 runs downwardly from building 60to septic tank 20, for primary processing. Wastewater from an unshownsanitary appliance or other source is introduced into inlet end 62 ofthe wastewater line. Gases, which come up the wastewater line from theseptic tank, are vented through stack vent 58 which protrudes above thebuilding roof When wastewater 64 flows into the septic tank, baffles 66prevent floating solids from moving out of the tank an into the firstpart of the distribution subsystem, effluent exit pipe 22. The primarilytreated wastewater flows from the septic tank, through check valve 70,into distribution box 30, and then into leach field 40 which iscomprised of several parallel strings of leaching chambers 34, one ofwhich strings is shown. Blower 71 causes pressurized air, drawn throughair inlet pipe 72 to flow down air pipeline 68 and into the distributionbox. Check valve 74 protects the blower from back flow of wastewater andsmelly gas when it is not in operation. An odor-absorbing charcoalfilter may optionally be used with or without the check valve.

[0045] When the blower 71 is activated, the air pressure increases inthe leach field. Check valve 70 prevents flow backward up effluent line22. Referring to FIG. 4, with reference to FIG. 2 and FIG. 3, thepressure within the leaching chambers is raised sufficiently to causeflow of air through the biomat 44, if any, and through the portions ofthe trench walls to which air passing through the chamber walls hasaccess. The air flows into the influence zone 50. From there, the airmay flow in various directions within the soil 38, ultimately escapingfrom soil surface 42 to atmosphere. Thus air flows serially through theconduit interior, the trench wall, and the influence zone, in the samedirection as wastewater flows. Should there be a substantial quantity ofwater in the soil of the influence zone when the blower is started, thepressure of the air will desirably hasten the flow of water out of theinfluence zone. Some air may move directly upwardly from the trenchinterior to the surface. If the soil above the trench is saturated, asit may be in a severely failed leaching system, upward flow should behelpful in restoring the system. In experiments, it has been found thatupward air flow is not a particular problem. In many systems, the soiltends to be compacted above the trench, which inhibits such flow. Asdiscussed below, a barrier on or in the soil above a leach field trenchwill tend to inhibit upward flow.

[0046] The air flow into the conduit is maintained for a desired time,according to the result sought and obtained. After a time, air flow maybe ceased, so the system resumes its normal operation or, the system maybe used during the time of air flow, as described below. Typically, alow power centrifugal blower is sufficient for producing the pressuredifferential which induces flow through the soil. The means forproviding pressurized air will depend on the resistance of the air flowpath. A regenerative type blower is used if a relatively high pressureis needed. Alternately, other means for flowing air may be used, such asblowers, fans, compressors, etc., according to the air movingperformance required and the price of the component. Unless statedotherwise, all pressures stated herein are gage pressures, i.e.,relative to atmosphere.

[0047] Biomat is normally anaerobic. To the extent such is present, airflow will tend to make it at least temporarily aerobic, thus engenderingdesirably different biological or chemical reactions which alter andreduce the biomat. In one mode of the invention, air is forced into theinfluence zone and beyond, along the same general flow paths whichwastewater has. Obviously, to the extent the influence zone and adjacentsoil are saturated, there will be a physical/hydraulic effect, asforcing air into them will tend to unsaturate them. To the extent theinfluence zone is not appropriately aerobic, the flow of air tends tomake it so, both by physical displacement and by desirable biochemicalactivity. If there is an accumulation of oxygen-demanding constituentswithin the influence zone and surrounding soil, they will be desirablyoxidized and reduced in amount. To the extent there is excessundesirable gas in the soil, such as methane, carbon dioxide andhydrogen sulfide, they will be incorporated into the air stream andcarried away, e.g., by diffusion in accord with the law of partialpressures; and, the changed environment will selectively affect theirproduction.

[0048] Thus, in synopsis, the invention process maintains or improves,as the case may be, the function of a leach field by (a) a physical(mechanical, pneumatic, hydraulic) effect; and (b) a chemical and orbiological effect, which for simplicity if referred herein to as abiochemical effect, or in related fashion, to a change in biochemistry.

[0049] With respect to the biochemical effect, it is generally acceptedthat in a major way the efficacy of the influence zone in treatingwastewater depends on the soil within the zone comprising apredominantly aerobic environment, as such is contrasted with ananaerobic environment. In a typical failed system where for one reasonor another the influence zone is anaerobic, the capability for treatingwastewater is as little as one-tenth that of a desirable aerobicenvironment which enables aerobic metabolism and oxidation. An aerobicenvironment is said to exist when the oxygen tension is sufficient topredominantly sustain the growth of aerobic bacterium. See Chapter 10 ofthe textbook of R. Atlas, “Microbiology, Fundamentals and Applications,”MacMillan Publishing Co., New York (1984). For this description, anaerobic soil is one which is macroscopically aerobic, e.g., thepreponderance of the volume of the soil of interest has oxygen tensionsufficient for sustaining predominantly aerobic bacterium. An anaerobicsoil in this description is one which is not aerobic. Nonetheless,within a mass of aerobic soil, such as the influence zone, theenvironment may vary from point to point, and anaerobic conditions canexist within a predominantly aerobic environment. For example, anaerobicmicro-pores may be present within an array of aerobic macro-pores.

[0050] The gross environment in the influence zone can be looked at inanother way, according to principles of stoichiometry. As isconventional in wastewater flow analysis, wastewater can becharacterized according to Oxygen Demand. Oxygen Demand is acharacterization of how much oxygen is needed to effectively treat theoxidizable constituents in the wastewater to make them environmentallybenign. Oxygen Demand is usually divided into two constituents, namelyBiological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD). COD iscommonly measured by the so-called Hach Method 8000. For wastewatersystems associated with habitations, BOD is the commonly used parameterof interest. It is commonly measured in accord with United StatesEnvironmental Protection Agency Standard 405.1. Stoichiometry, asapplied here to oxygen demand, refers to the chemical balance between anoxidizable material and oxidizer, in this instance, within the influencezone. If the influence zone receives a quantity of air which isstoichiometric, it means the quantity is exactly that which is necessaryfor complete theoretical oxidization of the oxidizable matter in thezone. In real situations, there are imperfect mixing and otherinfluences, and to achieve full oxidation, some excess air (oxygen) isrequired. Thus, from this viewpoint, the desired aerobic influence zonewill be characterized by oxygen-bearing gas flow over time, e.g., hours,which is in substantial excess of stoichiometry for the oxidizableconstituents of the wastewater entering the zone over the same time. Theexcess stoichiometric air flow can derive from artificial means, such asthrough use of the invention, by natural means such as migration throughpermeable soil, or by a combination of those. As an example of suchpractice, for the system referred to in connection with Table 1, acontinuous flow of 280 l/minute of injected air provides 50-100 timesthe stoichiometric quantity for a typical about 1200 l/day wastewaterstream.

[0051] Accordingly, in the invention, air is characterized as an activegas. It maintains or alters the composition of constituents andbiochemistry of the influence zone. It contains oxygen and enablesoxidation. Accordingly, other active gases may be used with or insubstitution of air. For instance, oxygen or ozone enriched air may beused for better activity, and an oxygen-helium mixture may be used for acombination of greater fluidity and activity. Optionally, liquid orgaseous additives, such as reactive substances like hydrogen peroxide,surfactants, and the like, may be introduced into the air stream in line68 from additive system 76, by pumping or other obvious means. See FIG.4. Alternatively, they may be introduced separately into the leach fieldconduits at the distribution box, distribution pipes 56, or chambers.Included within the effects of such additives will be to promotewetting, to act as solvents, and to increase oxidization or to promoteother biochemical activity beyond what air induces.

[0052] Thus, in one aspect of the invention, an influence zone will besaturated with water and the pressure and flow within the soil of theinfluence zone is sufficient to unsaturate it. In another aspect of theinvention, an influence zone will initially have a composition that isdeficient in oxygen, being biochemically significantly less than thevolume percent oxygen in air, and it will be changed so it approximatesthe composition of air. For instance, a starting composition of 14-19%oxygen will be changed to 20-21%, at a point about 15 cm from the innerboundary of the influence zone. In another aspect of the invention, theinfluence zone and surrounding soil will have constituents, in additionto oxygen, which are substantially different from the composition ofair. For instance, carbon dioxide may exceed 2%, methane 1% and hydrogensulfide 0.005%. Use of the invention will change such values in thedirection of the composition of air.

[0053] In the invention process there will be a flow into the influencezone of a quantity of gas which is effective. That is, the quantity willproduce part or all of the above described desired physical or chemicalchange. Of course, the quantity or total mass of gas put into theinfluence zone is a product of the flow rate and time. The flow rate ofthe air within the soil profile will depend on the permeability of theparticular soil profile and the applied differential pressure.Generally, it is an object to keep the air mover small for purchase andoperating cost and noise reasons. Thus, in one mode an air mover is runcontinuously to pressurize the leach field, with or without simultaneoususe for wastewater. In another mode the air mover is run intermittently,either during periods of wastewater use, or in periods of non-use.

[0054] In a primary aspect of the invention, the amount of gas which isflowed into the influence zone is biochemically effective. Put anotherway, the air flow is sufficient in quantity to alter the biochemicalconditions in the influence zone from those conditions which would existin the absence of flowing, to a degree which is significant to thetreatment of wastewater and soil. What is meant by biochemical orbiochemistry is described above. Another primary aspect of the inventionis to physically move water from the influence zone and to replace it byair, to a degree sufficient to create an aerobic region in part or allof the influence zone and or to increase the permeability of the zone.What is an effective amount can vary with the starting condition in theinfluence zone. Thus, an effective amount of gas will change the zone sothat treatment of wastewater, which simultaneously or subsequentlyenters the zone, will be significantly better treated. Thus, one or moreof the following parameters will be meaningfully and significantlyaffected: the quantity of wastewater (e.g., volume and oxygen demand)which can be handled in a unit volume of influence zone will beincreased; the quality of the effluent from the influence zone will behigher in the context of common environmental standards for undergroundwater, the permeability of the zone will be increased; the pressurenecessary to cause a unit of gas flow through the zone will drop; thepressure gradient within the zone for a given flow of gas will drop; thezone will change in character from anaerobic to aerobic; the quantity ofwater resident in the zone at any given instant will decrease; thefraction of oxygen in the zone will increase; and, the fraction of gasesassociated with anaerobic activity, such as carbon dioxide, methane andhydrogen sulfide, will be decreased in the zone.

[0055] It follows from the foregoing, that to get a significant quantityof air flow there must be a commensurate significant pressuredifferential applied across the influence zone. Usually, it is desiredto effect the change in a short period—a matter of hours or days, whichmay lead the user toward higher pressures. A physical movement of waterwithin the zone usually occurs in a matter or minutes; and, asignificant change in biochemistry will usually occur in hours, and willapproach equilibrium in hours or days. The rate at which the beneficialeffects are achieved depend on the air pressure/flow, the initial andchanged conditions of the influence zone (e.g. permeability,temperature, etc.), any continuing introduction of new wastewater havingoxygen-demand, and so forth.

[0056] During use, the soil profile around a properly functioningwastewater system leach field will be moist, inasmuch as tension andcapillarity will cause water to be retained. Moisture provides a soilprofile with a flow resistance significantly greater than that of drysoil. Thus, simply flowing air down a conduit of a moist leach field,where the end of the conduit is vented to atmosphere, does not achievethe objects and benefits of the invention. While the environment withinthe conduit may be affected, there will be insufficient static pressurewithin the conduit to induce flow into the surrounding soil, owing tothe resistance of moist soil profile and biomat if any to flow.Obviously, if the influence zone is saturated, the chance for flow iseven more remote. Experiments with perforated pipe and leaching chambersburied in sand more permeable than typical soil, using fans like thosesuggested by the prior art, fail to induce biochemically or physicallyeffective flow into the influence zone. To obtain flow from apressurized conduit that will significantly affect the influence zone ofa typical leaching field within a matter of hours or days, in thedesired ways described herein, the conduit static pressure willpreferably be in the range 1-100 cm water column. Obviously, when aliquid is to be pushed from a saturated zone, the initial pressurerequired is higher than if there is no saturation. If there issaturation, and it is alleviated by air treatment, the necessarypressure drops. Likewise, when the biochemistry is changed, soilpermeability tends to be increased, and the necessary pressure drops.Experiments to date for a typical system, described in connection withTable 1 below, have been conducted. Relatively low pressures and perunit area mass flow rates occur in the influence zone and surroundingsoil. For instance, a blower providing 290-1400 l/minute at 2.5-100 cmwater column may effectively be used in a leach field having anestimated trench area sidewall and bottom area of 74 m². A nominal flowrate soil immediately adjacent the trench wall will be of the order of0.26-1.3 m³/m²/minute. After treatment, a Table 1 kind of system mightbe biochemically maintained by a continuous flow from a lower capacityblower, for instance one with capacity of 1700 l/minute operating atstatic pressure as low as about 2.5 mm water column. In mostapplications, on-going or maintenance pressures will probably be higher,so it will be desirable to have a blower that produces at least about7.5 cm water column pressure.

[0057] Differential pressure may be applied for many hours, extendinginto days or continuous operation, to achieve the desired effects. Thus,it can be very difficult to detect flow and pressure gradients, thepresence of which is inferred and implicit because there is a measurablechange in the gas content of the soil during use of the invention, asshown by the example below. The efficacy of the invention is often bestdetermined by desirable change in, or maintenance of, gas content of thesoil. In particular, oxygen is made high; carbon dioxide, methane,hydrogen sulfide and nitrogen compounds are made or kept low; all in thedirection of the content of atmospheric air or in a biochemicaldirection which is better than air for aerobic bacterium.

[0058] The apparatus in FIG. 4 may be modified somewhat to make analternate embodiment in which a vacuum, instead of pressure, is appliedto the distribution box, distribution pipes or chambers of the leachfield. Check valve 70A is replaced by a manual or motorized valve. Thevalve is closed during vacuum operation—assuming the vacuum level issuch that it would unacceptably draw the contents from the septic tank.Any liquid drawn toward the vacuum pump is appropriately trapped bycommon means, and the liquid is re-introduced into the wastewater lineor septic tank. When a vacuum is applied, air is drawn from the surfaceof the earth, through the soil, the influence zone, any biomat, and intothe chamber, in ways which will be appreciated from the otherdescription here. The air drawn from the system by the vacuum pump maybe exhausted to atmosphere. Thus, there is serial flow which is thereverse of that which is described when the conduit is pressurized. Theleaching system cannot be used for processing wastewater from the septictank during the time it is placed under vacuum.

[0059] With reference to FIG. 5, in another embodiment of the invention,one or more pressure-vacuum perforated pipes 72 (called auxiliary pipeshereafter) are installed, either as original equipment or as retrofit,in proximity to, and parallel to, the chamber-filled trenches 35. Air iseither drawn from the pipes 72 or forced into the pipes 72, so that theleach field is beneficially affected. In one mode, pipes 72 areconnected to a vacuum pump and gas is pulled from the soil. Appropriatecommon traps and trap emptying means are used to handle any wastewaterthat is drawn into the auxiliary pipes and to the pump, and the trappedwater is recycled to the septic tank or leach field. The evacuation ofpipes 72 pulls air from the chambers to the extent they are incommunication with atmosphere by means of vents in the distribution box(e.g., in substitution of line 68) or chambers, or through the septictank and stack vent 58, consistent with other discussion herein.

[0060] When auxiliary pipes are vented, air will be drawn from the earthsurface 42 downwardly through the soil 38, as indicated by arrows in theFigure, according to the vacuum level, the permeability of the soil andconditions inside the chambers. Preferably, there is significant flowthrough the chambers and trench walls, to replicate to a degree theeffect achieved when the chambers are pressurized, as described above inconnection with FIG. 4. To encourage such, auxiliary pipes 72 are placedsufficiently close to the trenches/chambers, and deep enough, to createa pressure gradient across the biomat if any and within the influencezone. As shown in FIG. 5, a membrane, such as plastic sheet 96, isoptionally placed in the soil profile above the pipes 72 to limitdownward flow of air in between the chambers. When the chambers are notvented to enable air flow directly from atmosphere to the chamberinterior, the membrane tends to cause the air to flow from surface 42towards, into and through, the chambers. In one alternative, themembrane is a layer of relatively impermeable natural material, laidwithin the indigenous soil. In another alternative, the membrane isplaced on the earth surface 42. Preferably, the membrane runssubstantially horizontally; in other modes, the membrane may runvertically or at an angle with or without a horizontal membrane. Instill another alternative, the surface of the earth is compacted orotherwise treated to lessen permeability and to thereby functionallycreate a membrane.

[0061]FIG. 6 shows a stone filled trench and pipe 72, together with acoordinated graph showing the estimated nominal variation in pressure Pversus depth from the surface. The pipe 72 is beneath and parallel to astone filled trench 35 and evacuated. A sub-atmospheric pressuregradient is established along the arbitrary vertical reference line D,as indicated by the dashed line P on the right side of the Figure. Thepressure gradient induces the air flow indicated by the arrows on theleft side part of the Figure. The air flows through the soil above thetrench, more freely through the spaces amongst the stones, and thenvertically down through the soil beneath the trench, and into the pipe.Corresponding pressure gradients and flows will be inferred for chambershaving evacuated auxiliary pipes directly below.

[0062] In an alternate embodiment of use construction in accord withFIG. 6, auxiliary pipes 72 are pressurized to thus create a positivepressure gradient and related flow within the soil. This will beessentially the inverse of the phenomena just described for evacuatedpipes. Thus, the pressure in the soil in vicinity of the trench,chamber, or pipe, as the case may be, will be supra-atmospheric and airwill flow into the pipe and upwardly through the soil profile to thechamber and or soil surface. When the pipes 72 are beneath the influencezone, pressure or upward air flow may also retard the downward flow andescape of wastewater to ground water, which could be either desirable orundesirable depending on reactions in the influence zone.

[0063]FIG. 7 is a fragmentary picture which will be understood from itsanalogy to FIG. 5. FIG. 7 shows one of a plurality of spaced apartvertical pipes 78, which is positioned adjacent one or more of thetrenches, along the length of the trench, in place of the horizontalpipes 72. The pipes 78 have perforated lower ends 79, to enable air toflow into and from the soil. As for other like Figures, the flow ofgases, according to whether the pipe is pressurized or evacuated, isindicated by the double-headed arrows. Pipes 78 may alternatively beangled downwardly so the lower pipe ends are positioned beneath thetrench, rather than adjacent to it as shown. Thus, the term “verticalpipe” will encompass pipes which are generally running in an upwarddirection, whether true vertical or at an angle to such, in which casethey are only generally vertical. The advantage of the use of verticalinjection or suction pipes is one of easy retrofit. Combinations ofhorizontal vertical (and angled) pipes and means for interconnectingthem to the source of pressure or vacuum will present themselves. Thehorizontal or vertical aeration pipes shown in FIG. 5 or 7, and thediffusers of FIG. 14 and 15 discussed below, may be installed proximateor within individual trenches, or portions thereof, rather thangenerally throughout an entire leaching system, to cope with a localizedproblem.

[0064] The operation of the FIG. 5 embodiment, as well as operation ofother embodiments of the invention, may be controlled as indicated bythe schematic control diagram portion of FIG. 5. The composition and orpressure of gas in the influence zone or soil adjacent the zone issensed using a gas sensor comprised of a probe 74 and an analyzer 76.The analyzer provides a first signal to controller unit 94 whichcompares the first signal to a desired reference point (characteristicof a desired reference gas composition or pressure) and provides asecond signal to the air mover 71, to thereby modulate flow of air to orfrom pipe 68 and pipes 72, according to the difference between the firstsignal and the reference point. The air flow may be modulated bystopping and starting the air mover, or by increasing or decreasing thepressure. Pressure is alternatively measured within the conduit orsomething connected to it, because as indicated, a drop in staticpressure for a given flow is a measure of leach field improvement. Thereference composition is selected in accord with the teachings herein.For instance, the reference composition may be such as 20% oxygen, orless than 1% carbon dioxide. The reference pressure is selected inrelationship to other parameters which measure the performance of theinfluence zone, and based on accumulated experience with like wastewatersystems.

[0065]FIG. 14 is a view like FIG. 3, showing a chamber having a oblongcross section pipe 94, called here a diffuser, buried at shallow depthbeneath the soil at the base of the chamber. Diffuser 94 may bealternatively laid on the soil at the base of the chamber. Diffuser 94is connected to a source of pressurized air, so pressurized air isforced into the chamber in an evenly distributed way, to achieve thedesired effect which has been described in connection with FIG. 5-7.FIG. 15 is like FIG. 14 and FIG. 3, showing a perforated wastewater pipe32 in a stone filled trench 35. Running along the length of the bottomof the trench are two small diameter auxiliary pipes 96 carryingpressurized air. In another alternative, the pipes 96 are shallowlyplaced in the soil 38 beneath the trench, in manner analogous to FIG.14.

[0066] Referring again to the FIG. 4, there is a further embodimentwhich is useful, when the leach field chambers are pressurized. Itcomprises using the characteristic of the septic tank outlet to providethe means which prevents the back flow of air toward the wastewater line18, instead of employing check valve 70. For instance, when the septictank outlet is an elbow, the head or water in the septic tank may resistback flow pressures of 2-100 cm water column. If the septic tank bydesign permits through-flow of air, such as when a tee fitting is usedinstead of an elbow, then the septic tank outlet or inlet may bemodified by blocking off the openings which permit air passage. Whenthese circumstances exist, the flow of wastewater into and out of theseptic tank may be maintained during air pressurization of the leachfield, assuming the resultant increase in head at the inlet end of theseptic tank is tolerable. This will be further understood by thediscussion which applies to the use of a water trap valve upstream ordownstream of the septic tank, below.

[0067] Another alternative system design is as follows. It is verycommon that a septic tank will enable unimpeded flow-through of gases,from outlet to inlet. When such is the case, the location of the checkvalve 70 shown in FIG. 4 for the pressurized leach field may be changed.It may be moved to wastewater line 18, upstream of the septic tank, andthe pressurized air line 68 may be connected between the valve and theseptic tank. FIG. 8 shows such a construction in semi-schematic fashion,comprising check valve 80 in wastewater line 18. Of course, the septictank cannot leak excessively out the top if this option is to bepractical. A check valve which is useful in this embodiment and othersdescribed is a common horizontal flap type check valve sold inconnection with PVC wastewater pipe of 7.5-10 cm diameter. Manually orpower actuated mechanical valves referred to herein are likewisecommercially available.

[0068] The side elevation semi-schematic view of FIG. 9 shows anotherway for preventing back flow which can be used in substitution of acheck valve, namely J-trap 82. The trap type is familiar for toilets andother plumbing appliances. Sometimes, it is referred to as a U-trap.Generally, the J- or U-type of traps, and any other functionalequivalent, is referred to hereafter as a water trap. As illustrated inFIG. 9, wastewater water is retained in the base of the J-shape contourof line 18. The asymmetrical nature of the J shape means that there ismore resistance to upstream flow of a fluid, compared to downstreamflow. Thus the J-trap is functions analogously to a check valve, inimpeding flow of air and water in the downstream direction more than inthe other direction. Obviously, the back flow resistance can be overcomeby raising the pressure sufficiently high, but so can a mechanical checkvalve be overcome by sufficiently high pressure. Obviously, the depth ofthe J can be used to set the head to which the downstream part of theseptic system can be subjected. In the generality of the inventioninvolving pressurization, the valve in the wastewater line functions tolimit upstream movement and the valve may be a mechanical or water trap.It will be appreciated that in certain circumstances a water trap valvemay be functionally sufficient and thus useful on the downstream side ofthe septic tank.

[0069]FIG. 10 is a semi-schematic elevation view of a variation on FIG.8. The primary wastewater line 18 is fitted with valve 80A. Bypasswastewater line 86, with associated bypass check valve 82, provides abypass around the valve 80A. Valve 80A is kept open during periods whenthere is no air pressurization of the system, i.e., during use of thewastewater system as it takes place in absence of use of the invention.Thus, with appropriate pipeline angling and positioning, wastewater willnot consequentially pass through the check valve. This eliminatespossible noise that might be heard by occupants of the building, arisingfrom operation of check valve 82 as wastewater passes through.

[0070]FIG. 11 is a view like FIG. 10. It shows a plumbing arrangementwhich is useful when the pressure in the leach field, due to air flowingdown feed pipe 68, is more than the head of wastewater coming down thewastewater pipe can overcome. In such instance, the valve 80B in themain wastewater line 18A is closed. This causes wastewater coming downthe wastewater line 18 to accumulate in reservoir 84. By means of areservoir level sensor system, the pump 87 forces wastewater throughline 86 and forces it into the septic tank. Check valve 82B prevents anyback flow when the pump is not operating.

[0071]FIG. 12 is like FIG. 10 and shows still another plumbingvariation. Flow to reservoir 84 along bypass line 86 is controlled byvalve 82C. When the valve 82C is closed, wastewater flows along the mainwastewater line through check valve 82. When the valve 82C is opened,wastewater preferentially flows down line 86 into reservoir 84 fromwhence, according to signals from unshown sensors, the pump 87C isactivated to force wastewater down line 86C to overcome the air pressurein the wastewater system. The apparatuses described in connection withFIG. 10-12 may be alternatively installed in exit line 22 ordistribution line 56.

[0072] The elevation view of FIG. 13 shows how a centrifugal type blower71 can be placed in the stack vent line 58, when J-trap 92 (or afunctional substitute, e.g., a plurality of appliances having integraltraps), or a mechanical valve (e.g., on-off or flap-check), is presentto prevent back flow of pressurized air, up the wastewater line 18 intobuilding 60. When actuated, the blower forces air downwardly in thestack, and into the septic tank. When not actuated, the blower allowswastewater decomposition gases to escape up the stack. Particularly forretrofit purposes, the blower may be placed at the upper end of thestack vent, exterior of the building.

[0073] For original installation or retrofit purposes, a kit ofcomponents, which cooperate when installed, may be provided, e.g., to aninstaller of wastewater treatment system owner. The kit may comprise allor part of the following: a means for connecting an air flow supply to awastewater or a distribution line, a flow checking means, an air mover,and a control system.

[0074] In the most likely way in which the invention will be used, theleach field conduits will not be vented to atmosphere along theirlengths or at their ends farthest from the septic tank. However, theinvention can be applied to such kinds of vented conduits. When thechambers are pressurized, there is an obvious disadvantage in that theair mover has to have capacity sufficient to achieve the necessarystatic pressure while accommodating the loss of air out the vent.Alternately, the vents are fitted with valves. And, as has beenmentioned, in various modes of the invention, e.g. when the conduitshave subatmospheric pressure, it is contemplated that the conduits willbe vented through the septic tank and stack vent. For such modes, othervents into the conduits can have a positive or neutral effect.

[0075] The following is an example of the practice of the invention.Pressurized air was applied to the wastewater line of a long-functioningsingle family dwelling septic tank type system. Table 1 shows selectedrepresentative measurements of composition of soil profile gas contentand pressure over time. The septic tank permitted free flow-through ofair, thus the pressure in the leach field conduits was the same as atthe wastewater line. The leach field was comprised of two 30 m seriallyconnected lengths of perforated pipe in stone filled trench. Theindigenous soil was comprised of silt, with some clay and a trace offine sand and gravel. The soil temperature adjacent the trenches wasabout 13 degrees C. The arrangement was like that shown in FIG. 8, witha check valve 80 in the wastewater line. The air mover was a 93 w, 1700l/minute blower. Soil gas composition was measured using a commercialgas analyzer and a probe which inhibits infiltration of surface air. SeeU.S. Pat. No. 6,018,909. Pressure was measured with the same kind ofprobe. The applied positive pressure at the wastewater line wascontinuous and ended at the time shown for the readings. It graduallydeclined as the flow increased with the passage of time. Wastewater usewas continued during the test, with at an estimated 1200 l/day input.Readings S7S and S7D were taken in the influence zone, respectively atdepths of 30 and 75 cm from the earth surface at the end of a 30 m firsttrench length. Reading S1S was taken at the inlet end of the same firsttrench. All readings were taken at 15-30 cm from the inner boundary ofthe influence zone, that is, from the outer surface of the stone filledtrench, which was not well defined in the long-used system. Generally,subsurface pressure measurements can be quite variable, which is inlarge measure believed due to local variations in the essential soil.For instance, a horizontal worm hole may have a significant localeffect. The data in Table 1 represent typical or average data. They showhow the influence zone of the soil was desirably changed in the aerobicdirection over time and how unwanted constituents were decreased. Themethane reading for S6D is apparently anomalous. TABLE 1 Soil gascomposition change as a function of time for a pressurized septicsystem. Conduit Volume Percent Parts Per Million Influence Probe TimePressure Carbon Hydrogen Zone Pressure Location Hr mm H₂O Oxygen DioxideMethane Sulfide mm H₂O S7S 0 0 20.5 0.84 10 0 0 16 200 20.1 1.18 5 00.050 408 120 20.9 0.1 0 0 0.025 S6D 0 0 19.1 2.00 0 0 0 16 200 19.61.56 0 0 0.065 408 120 20.4 0.98 15 0 0.050 S1S 0 0 14.3 >5.00 0 0 0 16200 16.5 4.38 0 0 0.025 408 120 20.9 0.16 0 0 0.075

[0076] In other variations of the invention, air may be appliedcontinuously or discontinuously. Generally, it is desirable to limit theamount of time in which air is flowed, to decrease the cost of operatingthe blower or other air mover. Often, the dynamics of the system willpermit discontinuous air flow. In some instances, water is flowed inalternation with the flow of air or other active gas. In many instances,such as in the case of a domestic dwelling, wastewater flow varies overthe course of the day, and the time of flowing air may be varied incoordination with such. For example, a blower may be run for one hour ofpresumed non-use, during the nighttime hours. For another example, ablower may be run for two equally spaced apart half hour periods eachday. As in the examples, the time for airflow may be relatively small asa fraction of the total time of a wastewater flow day. In anotherapplication, a dosing pump or other means periodically delivers water tothe leach field from a septic tank or other sump.

[0077] In a further embodiment of the invention, the leach field isperiodically dosed with wastewater, sufficient to create ponding, or astanding water level, on top of the soil of the influence zone. Forexample, the inside of the conduit of FIG. 3 is supplied with water at arate and quantity such that it accumulates within the chamber on theunderlying influence zone. For another example, the trench of FIG. 2 islikewise supplied for a first period of time by flow through theperforated pipe, so that water accumulates to a certain level within thebroken stone of the trench. When the pond is created, the flow of wateris ceased. Then after some delay to allow natural percolation, oralternatively without delay, air pressure is applied to the conduit. Thepressure is maintained for a certain second time period, which may be amatter of a quarter hour, or more or less. The air pressure time issufficient to force the wastewater to flow through the influence zonedownwardly and otherwise, and to cause air to flow into the influencezone. Then the air pressure is ceased and the system is allowed toremain quiet for a third period of time, which period of time issubstantially greater, for example, two times or more greater, than thetime during which air was flowed. During the third period of time, theoxygen which is delivered by the airflow has a biochemically beneficialeffect within the influence zone, as has been previously described.Alternatively, the third time period may be essentially zero. Monitoringof system performance and the character of water exiting the influencezone will help determine what the third time period should be. Finally,the cycle is repeated again with another dosing of wastewater, nominallylike the first cycle.

[0078] In one mode of alternating air flow with water flow, engineeringjudgment is used to determine the times of flows and a simple cycletimer is used to control the system. In another mode, the wastewatersystem is fitted with a more elaborate control system comprising part orall of the following. A sensor, such as a float or other commercialliquid level sensor is installed in the void space. A signal from thesensor stops the inflow of water by the dosing pump, when the waterreaches a predetermined level. Immediately, or after a timer-controlledperiod, the blower is energized by the control system, to apply thepressurized air. Then, an oxygen sensor embedded in the influence zoneis used to determine when air has sufficiently flowed into the influencezone, and to stop the flow of air. A timer then determines when dosingis restarted. The timing and duration of dosing will obviously also be afunction of the wastewater which is flowed into the system.

[0079] In further practice of the invention, air is provided in anamount which is greatly in excess of the calculated amount which wouldbe theoretically necessary to satisfy the oxygen demand of the wastewater. Typically, such demand for a domestic dwelling will be primarilyBOD. The following is an illustration of such a situation. A system hasa flow of about 1140 l/day (about 300 gal/day) and a BOD of about 150mg/l, resulting in a calculated oxygen demand of about 0.17 kg/day. Airis flowed to the leach field at about 2.5 cm (1 inch) water columnpressure and about 285 l/min (10 cubic feet per minute) for one hour perday, so that the total air flow is about 17,000 l. Thus, there is a flowof about 4.5 kg of atmospheric oxygen through the system. And, theweight flow of oxygen gas was about 26 times the weight of BOD in thewaste water. The BOD of the wastewater exiting the influence zone istested and found to be about 1 to 5 mg/l.

[0080] In another example, a commercial establishment has a flow ofabout 1500 l/day (350-400 gal/day,) of about 1000 mg/l BOD to a leachfield. Air is supplied on a continuous basis at the rate of about 2850l/min (100 cubic feet per minute). Thus the input oxygen is about 1080kg/day while the oxygen demand of the wastewater is about 2.6 kg/day. Sothe flow of oxygen in the air is about 400 times the amount of oxygendemanded by the wastewater. In the generality of the invention, theairflow per unit time provides at least several times the theoreticaloxygen demand of wastewater per unit time. Typically, a unit of timethat is convenient is a 24 hour day.

[0081] While the septic tank system designs described herein are mostwidely used in connection with dwellings, the invention will be usefulin wastewater systems which process wastewater streams from industrial,agricultural, food processing, commercial, etc., operations, whichwastewater streams present the same disposal problems as domesticwastewater from habitations. In a septic tank system, the septic tank isa unit for primary processing or treatment of wastewater and the leachfield provides secondary processing or treatment of the wastewater, assuch terms are well understood in the art. Septic tanks are commonlyknown to comprise predominantly anaerobic environments. The inventionwill also be useful with leach fields which derive wastewater from othersources than primary units. Other devices, both aerobic and anaerobic,may be substituted for septic tanks as the primary (treatment) unit. Forinstance, an aerobic reactor which agitates the wastewater with air maybe used.

[0082] Although this invention has been shown and described with respectto a preferred embodiment, it will be understood by those skilled inthis art that various changes in form and detail thereof may be madewithout departing from the spirit and scope of the claimed invention.

I claim:
 1. A method of subsurface sewage treatment, wherein waste wateris flowed from a conduit into an influence zone within soil, in whichzone the biochemistry of the waste water is changed by biochemicalactivity, toward being environmentally benign, and wherein said wastewater is then flowed within the soil away from the influence zone, whichcomprises creating a significant gas pressure differential within theinfluence zone, to thereby flow a biochemically or physically effectiveamount of gas comprised of air or other active gas within the influencezone.
 2. The method of claim 1, wherein the gas flow is sufficient tocause the composition of the gas within the influence zone tosignificantly differ from the composition of gas which is otherwisepresent in the influence zone, in absence of said gas flow.
 3. Themethod of claim 2, wherein the influence zone is changed from anaerobicto aerobic.
 4. The method of claim 2, wherein the measured oxygen in theinfluence zone at a point about 15 cm from the inner boundary of theinfluence zone is increased from less than about 20 weight percent toabout 20 weight percent or more.
 5. The method of claim 1 wherein saidgas is flowed simultaneously with, and in the same direction as, theflow of wastewater.
 6. The method of claim 1 wherein, for a unit time,the amount of air or other active gas which is flowed contains severaltimes the calculated weight amount of oxygen which would theoreticallysatisfy the oxygen demand of the wastewater which is flowed into thesystem and then the influence zone.
 7. The method of claim 1 wherein theunit time is a day and wherein the oxygen which is flowed in with thegas is at least 10 times that which would theoretically satisfy saidoxygen demand.
 8. The method of claim 7, wherein the oxygen demand,measured in terms of BOD, of the wastewater is at least about 100milligrams per liter, and wherein the flow of oxygen in the gas is atleast about 2500 milligrams per liter.
 9. The method of claim 1, whereinthe significant pressure differential is created by a blower.
 10. Themethod of claim 1 wherein the gas pressure within the influence zone isat least about 0.03 mm water column above atmosphere at a point about 15cm from the inner boundary of the influence zone.
 11. The method ofclaim 10 wherein said gas pressure is at least about 0.08 mm.
 12. Themethod of claim 1, wherein at least a portion of the wastewater flowsvertically downward through the influence zone from a void spacethereabove, which void space is within or below said conduit, whichmethod further comprises: (a) flowing wastewater into the void space sothat it flows into the influence zone for a first period of time; (b)providing pressurized air to the void space for a second period of time,to thereby impel water through the influence zone; (c) ceasing saidproviding of pressurized air for a third period of time, to enable theair pressure in the void space to naturally dissipate; and, (d)repeating step (a) again.
 13. The method of claim 12wherein said steps(a), (b), (c), and (d) are repeated a multiplicity of times.
 14. Themethod of claim 12 wherein said third time period of step (c) is atleast two times greater than said second time period of step (b)
 15. Themethod of claim 14, wherein said third time period is about one hour andsaid first time period is less than about one quarter hour.
 16. Themethod of claim 12 which further comprises the steps of: (e) sensing thelevel of water within the void space, and generating a signal responsiveto such, (f) flowing wastewater into the void space at a rate and amountsufficient to cause water to accumulate within the void space and riseto a first liquid level, whereby a first level of water signal isgenerated; and, (g) ceasing the flowing of wastewater and providingpressurized air in response to said first level of water signal.
 17. Themethod of claim 16 wherein said steps (a) through (g) are repeated amultiplicity of times.
 18. A method of rejuvenating a subsurfacewastewater treatment system, wherein waste water is flowed from aconduit into an influence zone in the soil, in which zone thebiochemistry of the waste water is altered by biochemical activity,which comprises creating a significant gas pressure differential withinthe influence zone, to thereby flow a biochemically or physicallyeffective amount of gas comprised of air or other active gas into theinfluence zone.